Why are long-range forecasts less reliable?
Long-range forecasts are highly dependent on computer-generated numerical models. The models are based on a variety of weather elements, high-level circulation patterns, moisture, precipitation patterns and pressure fields. The atmosphere is very dynamic and is in constant motion meaning that the long-range computer models can change considerably from day to day. Initial errors in the computer models become larger over time, just like in archery where a small error in the arrows trajectory wont affect the accuracy when shooting over a short distance, but will cause the arrow to miss the target over a long distance. Long range forecasts can be thought of like a picture which is slightly out of focus. As we come closer to the forecast day, the picture becomes more focused and the forecast becomes more accurate.
